Evidence that selenium in rat sperm is associated with a cysteine‐rich structural protein of the mitochondrial capsules

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Abstract
The keratinous capsules surrounding rat sperm mitochondria were isolated 24 days after intratesticular injections of [75Se] selenite or [35S] cysteine. Dodecyl sulfate‐polyacrylamide gel electrophoresis of purified, doubly labeled mitochondrial capsules revealed only a single 75Se‐labeled component, whose molecular weight was 17,000, in agreement with previously reported observations obtained with cruder sperm fractions. Most of the 35S label and the major zone of stained protein on the gels coincided with the position of 75Se, suggesting that selenium is associated with a cysteine‐rich structural protein. The level of selenium in rat sperm, 195 ± 3.2 ng/108 sperm (approximately 30 ppm), determined by hydride generation and atomic absorption spectrophotometry, is consistent with a structural function for this trace element in the sperm.